Rhamnolipid emulsifying activity and emulsion stability: pH rules

Rhamnolipids have excellent emulsifying power with a variety of hydrocarbons, aromatic compounds and vegetable oils. This paper evaluates the effect of pH ranging from 3 to 9 on the emulsifying activity and stability of rhamnolipids and hydrophobic substrates (benzene, soybean oil and kerosene). Sodium dodecyl sulfate was used as a reference to compare the level of chemical and biological surfactant activity after 24 h (E(24)). The results indicate that pH exerts an influence over emulsion formation and stability. For rhamnolipids, peak emulsifying activity occurred under base conditions for all substrates,with the highest value achieved with kerosene at pH 8. The results of the present study demonstrate that rhamnolipids could replace chemical surfactants, such as SDS, in different industrial fields. (C) 2011 Elsevier B.V. All rights reserved.